This invention relates generally to pneumatic actuation devices and, more particularly, to a servo actuator that controls the flow of high pressure gases to a pneumatic actuator that is used in missile flight control systems.
Servo systems operating with high pressure fluids have been widely used in missile flight control systems to move control fins. Hydraulic or electro-mechanical devices have been used in the past but these devices have not provided many of the desired characteristics. In particular, servo systems using high pressure gases have used piston actuators, spool valves or open center poppet valves in the actuator control valve assembly. This control valve assembly interfaces between a pressure regulator and a pneumatic actuator that controls the fins. The valve functions to control the direction of gas flow to and from the actuator. The piston actuator has limited power and poor response, and the valves are inefficient because of gas leakage and do not offer low leakage at null.
Another type of prior valve used is the closed center four-way poppet valve. This valve is made by attaching two poppets to one stem and another two poppets to another stem. The opening and closing of the poppets is controlled by a camlike mechanism so that two poppets operate as inlet ports and the other two operate as outlet ports. This type of valve has generally poor operating smoothness due to lack of pressure balance or friction. These drawbacks necessitated a search for an improved actuator control device.